PRKN-linked familial Parkinson's disease: cellular and molecular mechanisms of disease-linked variants.

Parkinson's disease (PD) is a common and incurable neurodegenerative disorder that arises from the loss of dopaminergic neurons in the substantia nigra and is mainly characterized by progressive loss of motor function. Monogenic familial PD is associated with highly penetrant variants in specific genes, notably the PRKN gene, where homozygous or compound heterozygous loss-of-function variants predominate. PRKN encodes Parkin, an E3 ubiquitin-protein ligase important for protein ubiquitination and mitophagy of damaged mitochondria. Accordingly, Parkin plays a central role in mitochondrial quality control but is itself also subject to a strict protein quality control system that rapidly eliminates certain disease-linked Parkin variants. Here, we summarize the cellular and molecular functions of Parkin, highlighting the various mechanisms by which PRKN gene variants result in loss-of-function. We emphasize the importance of high-throughput assays and computational tools for the clinical classification of PRKN gene variants and how detailed insights into the pathogenic mechanisms of PRKN gene variants may impact the development of personalized therapeutics.

Mapping the degradation pathway of a disease-linked aspartoacylase variant.

Canavan disease is a severe progressive neurodegenerative disorder that is characterized by swelling and spongy degeneration of brain white matter. The disease is genetically linked to polymorphisms in the aspartoacylase (ASPA) gene, including the substitution C152W. ASPA C152W is associated with greatly reduced protein levels in cells, yet biophysical experiments suggest a wild-type like thermal stability. Here, we use ASPA C152W as a model to investigate the degradation pathway of a disease-causing protein variant. When we expressed ASPA C152W in Saccharomyces cerevisiae, we found a decreased steady state compared to wild-type ASPA as a result of increased proteasomal degradation. However, molecular dynamics simulations of ASPA C152W did not substantially deviate from wild-type ASPA, indicating that the native state is structurally preserved. Instead, we suggest that the C152W substitution interferes with the de novo folding pathway resulting in increased proteasomal degradation before reaching its stable conformation. Systematic mapping of the protein quality control components acting on misfolded and aggregation-prone species of C152W, revealed that the degradation is highly dependent on the molecular chaperone Hsp70, its co-chaperone Hsp110 as well as several quality control E3 ubiquitin-protein ligases, including Ubr1. In addition, the disaggregase Hsp104 facilitated refolding of aggregated ASPA C152W, while Cdc48 mediated degradation of insoluble ASPA protein. In human cells, ASPA C152W displayed increased proteasomal turnover that was similarly dependent on Hsp70 and Hsp110. Our findings underscore the use of yeast to determine the protein quality control components involved in the degradation of human pathogenic variants in order to identify potential therapeutic targets.

Folliculin variants linked to Birt-Hogg-Dubé syndrome are targeted for proteasomal degradation.

Germline mutations in the folliculin (FLCN) tumor suppressor gene are linked to Birt-Hogg-Dubé (BHD) syndrome, a dominantly inherited genetic disease characterized by predisposition to fibrofolliculomas, lung cysts, and renal cancer. Most BHD-linked FLCN variants include large deletions and splice site aberrations predicted to cause loss of function. The mechanisms by which missense variants and short in-frame deletions in FLCN trigger disease are unknown. Here, we present an integrated computational and experimental study that reveals that the majority of such disease-causing FLCN variants cause loss of function due to proteasomal degradation of the encoded FLCN protein, rather than directly ablating FLCN function. Accordingly, several different single-site FLCN variants are present at strongly reduced levels in cells. In line with our finding that FLCN variants are protein quality control targets, several are also highly insoluble and fail to associate with the FLCN-binding partners FNIP1 and FNIP2. The lack of FLCN binding leads to rapid proteasomal degradation of FNIP1 and FNIP2. Half of the tested FLCN variants are mislocalized in cells, and one variant (ΔE510) forms perinuclear protein aggregates. A yeast-based stability screen revealed that the deubiquitylating enzyme Ubp15/USP7 and molecular chaperones regulate the turnover of the FLCN variants. Lowering the temperature led to a stabilization of two FLCN missense proteins, and for one (R362C), function was re-established at low temperature. In conclusion, we propose that most BHD-linked FLCN missense variants and small in-frame deletions operate by causing misfolding and degradation of the FLCN protein, and that stabilization and resulting restoration of function may hold therapeutic potential of certain disease-linked variants. Our computational saturation scan encompassing both missense variants and single site deletions in FLCN may allow classification of rare FLCN variants of uncertain clinical significance.

Blocking protein quality control to counter hereditary cancers.

Inhibitors of molecular chaperones and the ubiquitin-proteasome system have already been clinically implemented to counter certain cancers, including multiple myeloma and mantle cell lymphoma. The efficacy of this treatment relies on genomic alterations in cancer cells causing a proteostatic imbalance, which makes them more dependent on protein quality control (PQC) mechanisms than normal cells. Accordingly, blocking PQC, e.g. by proteasome inhibitors, may cause a lethal proteotoxic crisis in cancer cells, while leaving normal cells unaffected. Evidence, however, suggests that the PQC system operates by following a better-safe-than-sorry principle and is thus prone to target proteins that are only slightly structurally perturbed, but still functional. Accordingly, implementing PQC inhibitors may also, through an entirely different mechanism, hold potential for other cancers. Several inherited cancer susceptibility syndromes, such as Lynch syndrome and von Hippel-Lindau disease, are caused by missense mutations in tumor suppressor genes, and in some cases, the resulting amino acid substitutions in the encoded proteins cause the cellular PQC system to target them for degradation, although they may still retain function. As a consequence of this over-meticulous PQC mechanism, the cell may end up with an insufficient amount of the abnormal, but functional, protein, which in turn leads to a loss-of-function phenotype and manifestation of the disease. Increasing the amounts of such proteins by stabilizing with chemical chaperones, or by targeting molecular chaperones or the ubiquitin-proteasome system, may thus avert or delay the disease onset. Here, we review the potential of targeting the PQC system in hereditary cancer susceptibility syndromes.

Experimental comparative study of a novel drug-eluting arteriovenous graft in a sheep model.

Background: Arteriovenous (AV) grafts often develop severe complications of stenosis due to neointimal proliferation that occurs either at the venous anastomosis site or at the outflow receiving vein. This study compares primary patency during 12 months of follow up for a new experimental Biomodics© interpenetrating polymer network (IPN) drug-eluting graft prototype with state-of-the-art GORE® ACUSEAL (ACUSEAL) in an AV graft model in sheep. Methods and results: An end-to-end bypass from the common carotid artery to the jugularis vein was performed bilaterally in 12 sheep. The usage of ACUSEAL or the IPN, both 6.0 mm in diameter, was determined via randomization. The sheep were followed up every 4 weeks with ultrasonic duplex scanning to determine patency; the experienced observer was blinded to the randomization. One sheep died after 11 days, and the final sample accordingly consisted of 11 animals. When comparing neointimal hyperplasia after 12 months in the two grafts, Fisher's exact test showed a significant difference with none out of 11 in the IPN grafts and 9 out of 11 in the ACUSEAL graft (p < 0.001). However, the Biomodics© IPN exhibited severe deterioration over time. Conclusions: Almost all of the grafts occluded during the 12 months of follow up. Although the zwitterion-bounded interpenetrating drug eluting polymer network showed signs to impair neointimal hyperplasia and thrombosis, age-related degeneration hindered demonstrating a potential improvement in patency.

A mutational atlas for Parkin proteostasis.

Proteostasis can be disturbed by mutations affecting folding and stability of the encoded protein. An example is the ubiquitin ligase Parkin, where gene variants result in autosomal recessive Parkinsonism. To uncover the pathological mechanism and provide comprehensive genotype-phenotype information, variant abundance by massively parallel sequencing (VAMP-seq) is leveraged to quantify the abundance of Parkin variants in cultured human cells. The resulting mutational map, covering 9219 out of the 9300 possible single-site amino acid substitutions and nonsense Parkin variants, shows that most low abundance variants are proteasome targets and are located within the structured domains of the protein. Half of the known disease-linked variants are found at low abundance. Systematic mapping of degradation signals (degrons) reveals an exposed degron region proximal to the so-called "activation element". This work provides examples of how missense variants may cause degradation either via destabilization of the native protein, or by introducing local signals for degradation.

Deep mutational scanning reveals a correlation between degradation and toxicity of thousands of aspartoacylase variants.

Unstable proteins are prone to form non-native interactions with other proteins and thereby may become toxic. To mitigate this, destabilized proteins are targeted by the protein quality control network. Here we present systematic studies of the cytosolic aspartoacylase, ASPA, where variants are linked to Canavan disease, a lethal neurological disorder. We determine the abundance of 6152 of the 6260 ( ~ 98%) possible single amino acid substitutions and nonsense ASPA variants in human cells. Most low abundance variants are degraded through the ubiquitin-proteasome pathway and become toxic upon prolonged expression. The data correlates with predicted changes in thermodynamic stability, evolutionary conservation, and separate disease-linked variants from benign variants. Mapping of degradation signals (degrons) shows that these are often buried and the C-terminal region functions as a degron. The data can be used to interpret Canavan disease variants and provide insight into the relationship between protein stability, degradation and cell fitness.

Exposure to tetrachloroethylene in dry cleaning shops in the Nordic countries.

OBJECTIVES: Tetrachloroethylene is the dominant solvent used in dry cleaning worldwide and many workers are potentially exposed. We report here on results of 1296 measurements of tetrachloroethylene undertaken in Nordic dry cleaning shops 1947-2001. METHODS: We searched documents and files in the Nordic institutes of occupational health for air measurements of tetrachloroethylene. Repeated measurements from the same facility during a short time interval were registered only once using the time-weighted average. We registered also changes over time in occupational exposure limits (OELs) to tetrachloroethylene. RESULTS: Only scattered measurements were available from the early years, and the exposure level seemed fairly stable up until the mid 1970s. The median exposure level was 20 p.p.m. in 1976 and decreased to 3 p.p.m. in 2000. Exposure levels in the four Nordic countries followed similar trends. In the late 1960s, the OELs varied between the Nordic countries from 30 to 100 p.p.m. Sweden was first to lower the limit, but limits gradually converged over time. At present, Denmark, Finland, and Sweden use 10 p.p.m., while Norway uses 6 p.p.m. Over time, the average observed exposure level was lower than the OEL in all countries, but in Denmark and Sweden, up to one-third of measured exposures exceeded the OEL. Overall, the stationary measurements for maintenance work showed 36 p.p.m., while the personal measurements showed 7.5 p.p.m. for dry cleaners and 6.25 p.p.m. for shop assistants. CONCLUSION: The Nordic data illustrate that it is possible over time to control chemical exposures even in an industry consisting of many small and scattered work places.

The transposed femoral vein arteriovenous fistula for hemodialysis.

INTRODUCTION:: The prevalence and incidence of patients in need of hemodialysis worldwide are increasing. The population in need of hemodialysis is becoming older and vascular comorbidities are more frequent than decades ago. Consequently, the prevalence of patients with exhausted possibilities of upper limb vascular accesses increases. In contrast to other lower limb vascular accesses, a fistula by transposing the femoral vein to the superficial femoral artery promises better patency rates in preliminary series. METHODS:: The first seven cases performed between October 2015 and March 2017 at the only center in Denmark performing this procedure were reviewed regarding demographics, comorbidities, complications, and patency. RESULTS:: The study population consisted of five males and two females, with a mean age of 61.6 ± 9.9 years, mean body mass index 24.9 ± 2.6, with various causes of uremia. Five patients (71.4%) experienced at least one complication, such as wound dehiscence, lymphocele, infection, hematoma, or steal. First cannulation of the transposing the femoral vein to the superficial femoral artery was conducted after 12.2 ± 4.3 weeks. Postoperatively, the patients have been followed 16.4 ± 9.6 months in the dialysis center. All but one is still using their transposing the femoral vein to the superficial femoral artery for dialysis, but three of these needed revision to maintain patency giving a primary and primary-assisted patency of 42.9 (95% confidence interval: 15.8-75.0) and 85.7 (95% confidence interval: 48.7-97.4), respectively. CONCLUSION:: Although postoperative complications and need for revision to maintain patency persists, our experience suggests that this is a feasible method when it is no longer possible to create an upper extremity vascular access. A learning curve for the entire vascular access team must be expected.

Protein stability and degradation in health and disease.

The cellular proteome performs highly varied functions to sustain life. Since most of these functions require proteins to fold properly, they can be impaired by mutations that affect protein structure, leading to diseases such as Alzheimer's disease, cystic fibrosis, and Lynch syndrome. The cell has evolved an intricate protein quality control (PQC) system that includes degradation pathways and a multitude of molecular chaperones and co-chaperones, all working together to catalyze the refolding or removal of aberrant proteins. Thus, the PQC system limits the harmful consequences of dysfunctional proteins, including those arising from disease-causing mutations. This complex system is still not fully understood. In particular the structural and sequence motifs that, when exposed, trigger degradation of misfolded proteins are currently under investigation. Moreover, several attempts are being made to activate or inhibit parts of the PQC system as a treatment for diseases. Here, we briefly review the present knowledge on the PQC system and list current strategies that are employed to exploit the system in disease treatment.

[Femoral vein transposition arteriovenous fistula for haemodialysis].

An upper extremity vascular access (VA) is preferred for haemodialysis, but when the central veins are occluded or all opportunities are exhausted, a lower extremity VA is necessary. Transposition of the superficial femoral vein is a durable arteriovenous fistula and should be the first choice in patients with long expected remaining lifetime. Peripheral arterial disease and heart failure are contraindications, and careful selection of the patients is mandatory. There is a risk of ischaemic steal and an even higher risk of wound complications. It is recommended, that the procedure is centralised.

[Mycotic aorta aneurysm treated with an autologous venous graft].

Systemic side effects, including sepsis, due to bacille Calmette-Guérin treatment for carcinoma in situ in the bladder, are observed in 15% of the patients. In rare cases, patients have developed systemic infections and mycotic aneurysms. In this case report, a 72-year-old man developed a mycotic aortic aneurysm, and the appropriate tuberculostatic drugs had no effect on his systemic infection. He was successfully treated surgically, replacing the affected aortic segment with an autologous venous graft, resulting in complete remission. A follow-up PET-CT three months later showed no sign of ongoing aortic infection.

Cancer in persons working in dry cleaning in the Nordic countries.

U.S. studies have reported an increased risk of esophageal and some other cancers in dry cleaners exposed to tetrachloroethylene. We investigated whether the U.S. findings could be reproduced in the Nordic countries using a series of case-control studies nested in cohorts of laundry and dry-cleaning workers identified from the 1970 censuses in Denmark, Norway, Sweden, and Finland. Dry-cleaning work in the Nordic countries during the period when tetrachloroethylene was the dominant solvent was not associated with an increased risk of esophageal cancer [rate ratio (RR) = 0.76; 95% confidence interval (CI), 0.34-1.69], but our study was hampered by some unclassifiable cases. The risks of cancer of the gastric cardia, liver, pancreas, and kidney and non-Hodgkin lymphoma were not significantly increased. Assistants in dry-cleaning shops had a borderline significant excess risk of cervical cancer not found in women directly involved in dry cleaning. We found an excess risk of bladder cancer (RR = 1.44; 95% CI, 1.07-1.93) not associated with length of employment. The finding of no excess risk of esophageal cancer in Nordic dry cleaners differs from U.S. findings. Chance, differences in level of exposure to tetrachloroethylene, and confounding may explain the findings. The overall evidence on bladder cancer in dry cleaners is equivocal.

What happens when organization of cervical cancer screening is delayed or stopped?

OBJECTIVES: Many countries rely on opportunistic screening, and data on its effectiveness are asked for. We assessed the impact on cervical cancer incidence and mortality of opportunistic screening compared with organized screening. SETTING: Women aged 30-64 in Denmark, 1973-2002; 16 counties with different screening strategies. METHODS: Cumulative incidence and mortality rates for women aged 30-64 by county. Poisson regression of incidence and mortality rates by age, calendar period and county. Interaction between type of county and calendar period measured the difference between counties with screening organized early versus late in time. RESULTS: A statistically significant interaction was found between type of county and calendar period (P=0.0151) for cervical cancer incidence, but not for cervical cancer mortality (P=0.9593). The interaction terms were not statistically significant when a comparison was made between a single county in which an organized programme was interrupted for an 11-year period and other counties. There was, however, a statistically significant increased incidence and mortality rates at the restart of the organized programme. CONCLUSION: Organization of cervical cancer screening accelerated the decline in cervical cancer incidence, compared with the trend in areas relying on opportunistic screening. No impact could be measured of the screening organization on cervical cancer mortality. A decade long stop of an organized screening programme was associated with a temporary increase in cervical cancer incidence and mortality. Coverage remains a key quality indicator in the ongoing modernization of screening technology.

Occupational risks for uveal melanoma results from a case-control study in nine European countries.

OBJECTIVE: Uveal melanoma is a rare disease with poor prognosis and largely unknown etiology. We studied potential occupational risk factors. METHODS: A population based case-control study was undertaken during 1995-1997 in nine European countries using population and colon cancer controls with personal interviews. Occupational exposure to sunlight and artificial UV radiation was assessed with a job exposure matrix. In total, 320 uveal melanoma cases were eligible at pathology review, and 292 cases were interviewed, participation 91%. Out of 3357 population controls, 2062 were interviewed, 61%, and out of 1272 cancer controls 1094 were interviewed, 86%. RESULTS: Using population controls, occupational exposure to sunlight was not associated with an increased risk (RR=1.24, 95% CI=0.88-1.74), while an excess risk found with use of colon cancer controls was attributed to confounding factors. An excess risk in welders was restricted to the French part of the data. Cooks, RR=2.40; cleaners, RR 2.15; and laundry workers, RR=3.14, were at increased risk of uveal melanoma. CONCLUSION: Our study does overall not support an association between occupational sunlight exposure and risk of uveal melanoma. The finding of an excess risk of eye melanoma in cooks in several European countries is intriguing.

Growth hormone receptor expression and function in pituitary adenomas.

OBJECTIVE AND DESIGN: Hypopituitarism, in particular GH deficiency, is prevalent in patients with clinically nonfunctioning pituitary adenomas (NFPAs) both before and after surgery. The factors regulating the growth of pituitary adenomas in general and residual tumour tissue in particular are not fully characterized, and the effect of GH and IGF-I on human pituitary cell proliferation has not previously been reported. In NFPA tissue from 14 patients we evaluated GH receptor (GHR) expression and signal transduction, and the effect of GH and IGF-I exposure on cell proliferation and hormone secretion in vitro. MEASUREMENTS: Tissue samples from 14 NFPAs were investigated. Expression of GHR in tissue samples was assessed by reverse transcription polymerase chain reaction (RT-PCR). Six tumours were immunostained with a GHR antibody. In the cell cultures, STAT5 (signal transducer and activator of transcription 5) phosphorylation was measured by Western blot analysis as an index of GHR signalling; cell proliferation was evaluated by [H3]-thymidine incorporation and glycoprotein hormone production analysed by radioimmunoassay (RIA). RESULTS: All adenomas investigated expressed the GHR, but there was no detection of STAT5 phosphorylation. Overall, GH and IGF-I administration did not significantly stimulate cell proliferation in vitro, although some individual adenomas exhibited a proliferative response to various extents. GH also did not significantly influence glycoprotein hormone secretion in vitro. CONCLUSION: GH receptors are expressed in human pituitary adenoma cells but their functional role is uncertain. GH and IGF-I do not consistently influence the proliferation of cultured pituitary adenoma cells.